Method of producing carbon granules



0a. 250, 1931. R, S, HOWARD 1,828,046 Y METHOD 0 RRRRRRRRRRRRRRRRRRRRRRR ES Filed April 12, 1928 atented Oct 20, 1931 j UNITED STATES LNPATENT OFFICE RUSSELL SAMUEL HOWARD, OF LA. GRANGE, ILLINOIS, ASSIGNOR TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF N'EW YORK, A CORPORATION 01 NEW YORK :HE'IHOD OF PRODUCING CARBON GRAN'O'LES I Application filed April .12,

. to obtain uniform microphonic properties.

In some instances where irregularly shaped particles-have been used there is a tendency for the sharp points of the carbon to penetrate the thin walls of the container of the unit and thus cause a leakage of the carbon from the container, thereby impairing the 'efliciency of the unit.

It is an object of. an economical method for producing hard carbon in a very efiicient form for use in varij able resistance units.

In accordance with the general features of the invention, hard spherical carbon granules are repared from synthetic resins commonly nown as condensation products,

which aregranulated and screened until particles of a predetermined size are obtained.

These particles are then placed upon a surface which they will-not wet and heated until they become molten. Since the surface has a high capillary repulsion for the particles, the particles are drawn into spherical form due to surface tension in which form they are bonized.

It is believed that a complete understanding of the invention may be had by reference to the following description taken in conjunction with the accompanying drawings, in

which Fig. 1 illustrates an apparatus for melting the particles, and

Fig. 2 is an enlarged view of a number of spherical particles on a surface upon which they were molten. i

In practicing the method the particles which are to be carbonized are,preferably prepared from synthetic resins commonly known as phenolic condensation products, particularly the cresylic acid resins. A quantity of removable. A plurality of electric heating his invention 'to provide cooled and hardened and Subsequentlycar' which continuously. iSeS from about of the condensation products and drives out.

1928. Serial in. 2 9,503.

such material is crushed or granulated by any well known means to such a degree that alarge part of the material will consist of particles of the desired bulk or mass. The particles arethen screened to eliminate the 5 'oversized and undersized particles which may be remelted and used again.

The resin particles of the desired size are placed upon a surface which they will not wet when molten, such as an oxidized metal surface or preferably an asbestos surface. Fig. 1 illustrates an .oven 3 which may be used for this purpose having an asbestos plate 4 which is slidably mounted therein sov as to be readily elements 5 are located underneath the plate to uniformly heat the plate to the required temperature. The heating elements 5 may be, connected to any suitable source of current (not shown) through a rh'eostat 6. by which a close temperature control ma be obtained.

As soon as the resin particles I ecome molten they will be immediately formed into spherical granules whereupon the electrical. current may be interrupted by means of a switch 7 to allow the granules to cool and solidify'or the asbestos plate may-be withdrawn from the oven to cool and solidify the granules while another similar plate with resin par ticles is placed in the oven.

In order to carbonize the resinous condensation products they are heated first for about twenty to thirty hours to a temperature C. to

about 290 C. The heating may be carried on in an oven heated first by steam and then by gas combustion. This'stage of heating produces complete polymerization and hardening the gases. After the preliminary stage, the hardened resin is carbonized, the resin is preferably packed in a carbon or graphite 'containeranda protective material, such for example, as peat. The container packed in coke, lamp black, or the like, is slowly heated by gas combustion or electrically to ,a temperature rising'to about 700 C.-in about one week. The carbon is given a final firing at a temperature rising from 800 to 1100 C. in no a few hours, whereupon it is cooled and ready for use.

It has been found that s herical carbon granules formed as describe above are par- 5 ticularly well adapted for use in sound transmitting devices having what is known as a floating diaphragm which is resiliently supported. The spherical granules have no appreciable tendency to work their wa out of their container through the juncture tween the container and the diaphragm. When the spherical particles are used 1n variable resistance units. very satisfactory results are also obtained due to the fact that the spherical granules can conveniently be made of a substantially uniform size and therefore a I more uniform variationof the resistance will result.

It will be understood that the illustration of the invention herein described is merely a convenient and useful form of the inventlon which is capable of many other modifications without departing from the spirit and scope I of the invention.

What is claimed is: I 1.- A method of producing carbon granules *which comprises heating comminuted particles of a fusible solid phenolic condensation product out of contact with each other forasuificient length of time to harden them, and

then carbonizing the particles.

2. A method of producing spherical carbon granules which comprises placing comminuted particles ofa fusible solid phenolic condensation product in dispersed relation upon an asbestos surface, gradually raising thetemperature 'ofthe particles from about to about 290 C. over a period of from 20 to 30 hours to harden the particles, and carbonizing the hardened particles by gradualg raising their temperature to about 700 over a period of about one week.

3. A method of producing carbon granules which comprises rapidly heating particles of a fusible solid phenolic condensation product to melting out of contact with each other, then solidifying the molten particles by cooling the same, then hardening the particles by slowly heating them while maintaining them in separated relation, and then carbonizing the particles.

4. A method of producing carbon granules which comprises rapidly melting particles of a fusible solid phenolic condensation roduct into separate droplets out of contact with each other on a surface, then solidifying the resulting granules by chilling the same, then converting them without softening into fusible resin by heating the granules slowly, and then carbonizin the granules.

In witness wiereof, I hereunto subscribe my name this 29 day of March A. D. 1928. RUSSELL SAMUEL HOWARD. 

